An intake/exhaust valve, which opens and closes an intake/exhaust port of an internal combustion engine, is usually a poppet valve, which has a flat-conical shaped valve element and a valve stem extending from the center of the valve element. The valve element is provided in an opening, which is formed in a combustion chamber side of an intake/exhaust port formed in the cylinder head. The valve stem extends into the cylinder head and passes through the cylinder head, and the tip of the valve stem is in contact with a rocker arm provided above the cylinder head (PATENT DOCUMENT 1, for example). The rocker arm is swung by a cam formed on a cam shaft, so that the valve element opens and closes the intake/exhaust port.